Tire Rack sells black TPMS's i believe. They aren't listed regularly but popped up in a google search. Give them a call to see if they're available.
Alternativelly, on my Volk Racing wheels, I used these:
Mackin Industries » T.P.M.S Valve Stem Cover
Colored "sleeves" that go over the exposed portion of the TPMS valve stem. They are distributed through Mackin, so any retailer can get them, but they're made by some other company i have never heard of.
Be advised, THEY DO NOT FIT out of the box. They are maybe 5-10mm too long, which blocks proper mounting of the tpms valve stem. My shop was able to grind them down so they fit fine now. At $30 or so, they're cheap so if ur shop doesn't mind doing a little work then its an option.